From its structural standpoint1~2~, hinokitiol (4-isopropylcycloheptatriene-2, 4, 6-ol-2-one-1) is liable to undergo electrophilic substitution at 3, 5 and 7 (i. e., o, p and o' proposed by the authors). It follows, therefore, that hinokitiol would give 3 kinds of monoand di-substituted, and one of tri-substituted bromination products, Nozoe, Sebe and their coworkers3~ carried out the bromination of hinokitiol under various conditions, and obtained one kind of monobromo compound (m. p. 56°), two kinds of dibromo compounds (a m.p. 134°; ,8: m. p. 96°), and one kind of tribromo compound (m. p. 88°). From the course of formation of these compounds3~, and the measurement of dipole moments2~, it was assumed that monobromo compound (m. p. 56°) was substituted at 7 or o' (I), a-and /-dibromo compounds at 3, 7 (o, o') (II), and at 5, 7 (o', p) (III), respectively. Not only in this case, but also in the case of chloro and nitrocompounds, only two out of the three possible compounds of di-substituted products can be obtained. In short, the steric hindrance is so great in (IV) that, even if a di-substitution does occur, it is further brominated by the excess of the reagent, resulting in a tri-substituted compound (V).